It is a standard practice to provide controlled ventilation of enclosed spaces of buildings, such as crawl spaces and basements of the same, by use of ventilators located in suitable openings of the foundation enclosure walls. Such ventilators are generally provided with adjustable closure means, such as shutters or plates, to control the flow of air into and out of the enclosed space, depending upon temperature, weather conditions, and seasonal changes. Generally such foundation wall ventilators are affixed in the wall opening by cement or mortar during initial construction of the foundation wall.
Various types of ventilator constructions are known, the more common of which comprise a heavy metal rectangular frame having a metal grid, a screen across the grid, and a plate pivotally attached to the frame and movable by extension and retraction of an operating rod or lever to open and close the ventilating opening through the frame, as desired. It is also known to provide ventilator constructions having plural shutters or louvers which are pivotally movable from open to closed positions by temperature responsive springs to regulate the ventilation of foundation spaces.
More recently, it has been a practice to construct ventilators of molded plastic materials and parts to reduce the weight and/or cost of the ventilator.